The aim of this In Vitro study is to investigate the effects of alpha-MSH and related peptides (e.g., endorphins, neuropeptides) on osmoregulation. Atrial cardiocytes produce peptides (ANP's) that when released into the circulation causes a dramatic natriuretic and diuretic response. To date, it is not understood how the ANP's are released from the cardiocytes. We propose that ANP is under brain neuropeptide control and that this control plays an important role in osmoregulation and blood pressure. The neuropeptides alpha-MSH and beta-endorphin have been shown to be involved in osmoregulation. The natriuretic and diuretic effects of these neuropeptides are strikingly similar to those of ANP. There is evidence that ANP can be isolated from plasma of morphine-treated rats. This is suggestive of neuropeptide control of ANP release. We will test our hypothesis by employing perfusion, radioimmunoassay (RIA), high-performance liquid chromatography (HPLC), peptide chemistry, and bioassay. An In Vitro perifusion technique using rat right atrial cardiocytes will be used to test the ANP-releasing activity of alpha-MSH, beta-endorphin and related peptides. Appropriate antagonists of these peptides will also be tested. Perifusion fractions will be qualitatively and quantitatively analyzed for ANP-related material by RIA, HPLC, peptide chemistry and bioassay. These analyses will characterize the ANP- releasing activity of the neuropeptides and antagonists, as well as the ANP release mechanism. Additional the effect of ANP on the release of alpha-MSH and beta-endorphin from the pituitary will be studied by perifusion of neurointermediate cells. Perifusates will be analyzed for neuropeptide release by RIA, HPLC, peptide chemistry and bioassay. In addition to answering important questions related to osmoregulation, this study will provide a clearer understanding of the mechanism of ANP release. Additionally, it will be of significance to clarify whether the neuropeptide-ANP interaction is comparable in importance to the renin- angiotension-aldosterone system.